1. Field of the Invention
The present invention relates to a lens barrel, and in particular, relates to a retracting structure of the lens barrel.
2. Description of the Related Art
The assignee of the present invention has proposed a retracting structure of a zoom lens (zoom lens barrel) which enables a considerable reduction in length of the zoom lens. This retracting structure is disclosed in U.S. Pat. No. 7,013,081 (Japanese Patent No. 3,771,909). A feature of this zoom lens is that the length thereof in the retracted state is reduced by radially retracting (displacing) an optical element (retractable optical element) of the zoom lens system from an imaging (photographing) optical axis thereof while retracting the same optical element from a ready-to-photograph position along the imaging optical axis.
More specifically, in this type of zoom lens, the retractable optical element (e.g., a lens group) is supported by a movable frame therein which is guided linearly along the imaging optical axis in a manner to be movable between an on-axis position (where the optical axis of the retractable optical element coincides with the imaging optical axis) and an off-axis displaced position (where the optical axis of the retractable optical element is eccentrically positioned with respect to the imaging optical axis), and this movable frame is moved along the imaging optical axis by a rotational force of a rotational member such as a cam ring. In addition, the zoom lens is provided with a fixed cam member which moves the retractable optical element from the on-axis position to the off-axis displaced position by using a rearward moving force of the rotational member.
In addition, for the purpose of miniaturization of this type of lens barrel, United States Patent Application Publication No. 2006/0034604 A1 (Japanese Unexamined Patent Publication No. 2006-53444) has proposed a structure in which the rotational member is provided with an accommodation portion in which the retractable optical element is partly housed in the retracted state of the lens barrel. To prevent the retractable optical element and the rotational member from interfering with each other, the lens barrel is provided with a rotation limit mechanism (idle mechanism) which prevents rotational force from being transferred from a drive rotational member to the rotational member during a certain period of operating time in the lens barrel advancing direction from the retracted state toward a ready-to-photograph state of the zoom lens.
A subsequent study has revealed that there is still room for an improvement in operation accuracy in the rotation limit mechanism for the rotational member. Specifically, demands have arisen for an improvement in operation accuracy of movable members (e.g., the retractable optical element) associated with the rotational member by more precisely controlling the position and timing at which prevention of rotation of the rotational member commences and at which the rotational member is allowed to rotate, and for miniaturization of the lens barrel by reducing a safety margin for accommodating precision errors.